1. Technical Field
The current disclosure relates to liquid crystal systems that may be used in liquid crystal display elements. In particular, the disclosure relates to compositions including fullerene-containing complex nematic liquid crystal materials with high-speed electro-optical response, and liquid crystal devices using the disclosed composition.
2. Description of Related Art
Spatial light modulators (SLMs) with liquid crystal (LC) layers have been intensively investigated and improved over the last decade. The interest in these modulators used as liquid crystal display (LCD) elements arises from their beneficial characteristics, such as low operating voltage, good threshold characteristics, high uniformity, as well as enhanced grayscale, resolution, and speed characteristics.
Among different types of LC SLMs, study and development of dispersed liquid crystals (DLCs) hold great promise, because they combine the properties of photosensitive components with electro-optical parameters of LCs. Moreover, LC orients suspended particles within to act as molecular matrices which are easily controlled by external electric or light fields. The particles become sensitive to driving voltage and, as a result, the speed of liquid-crystal matrix orientation changes.
It should be noted that the electro-optical response speed is a very important characteristic of liquid crystal devices, since it influences the speed and correctness of the transformation of information processing. Different techniques may be used to enhance the speed of the electro-optical response. In addition to changing geometric dimensions of the structure and characteristics of the supply voltage, the physical-chemical properties of nematic liquid crystal materials (nematic LC) may be modified.
In particular, photosensitive substances (e.g. dyes) are being introduced into nematic LC materials. Introduction of these substances results in the increase of compound absorption and photoconductivity. In this case, the photorefractive effect is observed, resulting in an efficient modulation of a laser beam transmitted through LC sensitized with the dye, as outlined in Cipparrone, G.; Mazzulla, A.; Simoni, F. “Orientational gratings in dye-doped polymer-dispersed liquid crystals induced by the photorefractive effect”, Optics Letters, vol. 23, no.19, pp. 1505-7 (1998), (referred to as “Mazzulla” herein). Based on the effect indicated in Mazulla, switching times close to 5 ms have been observed. The defects of DLCs with dyes are poor light stability and inadequate speed.
A new technique uses NLCs sensitized with fullerenes to improve the nematic LC time-on and time-off characteristics of the electro-optical response. The experimental investigation of this method, the start of the model to reorient the LC-dipoles, and the influences of the boundary conditions are shown in some of the current inventor's papers; for example, in N. V. Kamanina, L. N. Kaporskii, “The effect of fullerenes on the dynamic characteristics of liquid crystal systems”, Tech. Phys. Lett. v. 26, no. 10, pp. 864-866 (2000), N. V. Kamanina, N. A. Vasilenko, “LC SLM based on fullerene doped polyimide”, Nonlinear Optics, v. 25, pp. 207-212 (2000), L. P. Rakcheeva, N. V. Kamanina, “Prospects of the use of fullerenes for the orientation of liquid-crystalline compositions”, Tech. Phys. Lett., v. 28, no.6, pp. 457-460 (2002), and N. V. Kamanina, “Optical investigations of a C70-doped 2-cyclooctylamino-5-nitropyridine-liquid crystal system”, J. Optics A: Pure and Applied Optics, v. 4, no. 4, pp. 571-574 (2002) (referred to herein as “Kamanina 2002”).
The systems contained three components: LC, sensitizer, and plasticizer. The mechanism used to orient LC dipoles involves creation of the wall from fullerene and fullerene-complex. This mechanism can be useful in orienting LC molecules, and can be easily formed and controlled under external action. In particular, it may be controlled using an electric field or light irradiation.
Switching times of less than 1 ms have been measured. The influence of the interface condition on dynamic characteristics of the LC mesophase, the nature of the alignment layer, and the affect of the applied voltage has been studied.
Moreover, it had been mentioned in Kamanina 2002 that the new technique for improving the switching parameters of the NLC electro-optical response could be useful in developing new LC displays. The enhanced local polarizability of a unit volume of media based on charge-transfer complex: pyridine group molecule-fullerene, introduced in NLC, has been calculated. However, a drawback of this technique is that the use of plasticizer as an additional component decreased the speed.
Further, in N. V. Kamanina and A. I. Plekhanov, “Mechanisms of optical limiting in fullerene-doped π-conjugated organic structures demonstrated with polyimide and COANP molecules”, Optics and Spectroscopy, v. 93, no. 3, pp. 408-415 (2002) and N. V. Kamanina, E. F. Sheka, “Optical limiters and diffraction elements based on a COANP-fullerene system: Nonlinear optical properties and quantum-chemical simulation”, Optics and Spectroscopy, v. 96, no. 4, pp. 599-612 (2004), evidence of charge transfer complex formation and the influence of this process on the absorption, nonlinear, and dynamic properties of pyridine and polyimide molecules was noted.
Additionally, some steps had been devoted to the study of charge transfer complex of different organic structures, and some work had been done showing the influence of charge transfer complex on the speed of NLCs. These steps are outlined in N. V. Kamanina, D. A. Moskovskikh, I. Yu. Denisyuk, M. M. Mikhailova, S. V. Butyanov, V. G. Pogareva, A. V. Mezenov, Yu. A. Zubtsova, V. A. Shulev, and I. Yu. Sapurina “The new internal orienting substituent effect-significant acceleration of the rotational rate of the molecules of a liquid crystal when fullerene-containing complexes are introduced into it”, Journal of Optical Technology, v. 71, no. 3, pp. 187-191 (2004), N. V. Kamanina, I. Y. Denisyuk, “Switching of optical response in fullerene-doped liquid crystal compounds”, Optics Communications, v. 235, nos. 4-6, pp. 361-364 (2004), and N. V. Kamanina, I. Yu. Denisyuk, M. M. Mikhailova, I. Yu. Sapurina, “Study of the time parameters of fullerene-containing nematic liquid-crystal cells: a nematic-smectic transition stimulated by a complex-formation process”, Journal of Optical Technology, v. 71, no. 5, pp. 327-329 (2004). Switching times of 200-500 microseconds have been measured.
It has been shown that the charge-transfer complexes between an organic donor and fullerenes drastically influences the dynamic properties of LCs with pyridine, polyaniline, phthalocyanine, etc. The new complex has a large dipole moment and hence the polarizability of the compound is increased. This effect improves the control of the nematic LC structure with high speed.
It is noted that previously, smectic ferroelectric liquid crystal structures have been used to improve the speed of LC-displays. However, alignment problems with smectic LC layers have been observed. Moreover, until now, smectic LC structures have been very expensive. The problems mentioned above affect the industrial application and development of ferroelectric LCDs.